As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in sealed packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and scaled longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
Once formed, the above packages may undergo further processing, such as the application of a reclosable opening device.
At present, the most commonly marketed opening devices comprise a frame defining a pour opening and fitted about a hole or a pierceable or removable portion of a top wall of the package; and a cap hinged or screwed to the frame, and which is removable to open the package. Alternatively, other types of opening, e.g. slide-open, devices are also known to be used.
The pierceable portion of the package may be defined, for example, by a so-called “prelaminated” hole, i.e. a hole formed in the base layer of the packaging material before covering the base layer with the layer of barrier material, which is therefore whole and closes the hole to ensure airtight, aseptic sealing, while still being easily pierceable.
In the case of aseptic packaging machines, the opening devices described, once formed, are normally applied directly to the packages by on-line application units located downstream from the packaging machine.
Application of the opening devices, e.g. by heat sealing or gluing, involves various preliminary operations on both the packages and the opening devices themselves. More specifically, when the opening devices are applied by heat sealing, both the heat-seal outer layer of the packaging material about the holes or pierceable portions of the packages and the opening devices are partly melted or softened locally by preheating.
Once applied to the respective packages, the opening devices must be held firmly on the packages long enough for the contacting materials to cool and to permit adhesion.
Similarly, when the opening devices are glued on, one or both of the parts for gluing must be coated with adhesive, and the parts must be held firmly in contact with each other long enough to permit adhesion.
Application units are known which substantially comprise two, e.g. chain, conveyors for successively feeding the opening devices and the packages respectively along separate endless paths having respective adjacent parallel portions, along which each opening device is glued to the respective package.
Alternatively, application units are known, e.g. as described in Patent EP-A-1462370, which comprise a first linear step conveyor for feeding a succession of packages along a first, preferably straight, path; a second linear step conveyor for feeding a succession of opening devices along a second straight path extending parallel and in the opposite direction to the first path; and a step-operated carousel conveyor for feeding the opening devices from a pickup station, coincident with one of the stop stations on the second conveyor, to an application station, where the opening devices are applied to the respective packages, and which coincides with one of the stop stations on the first conveyor.
More specifically, the carousel conveyor feeds the opening devices along a circular path, with a vertical axis, through a number of intermediate work stations, where the opening devices are arrested and undergo various preliminary operations before being applied to the respective packages.
In both cases, the versatility of known application units is fairly poor, on account of being unable to operate with different types of heating or adhesive application processes or different types of opening devices. For example, simply changing the way in which the adhesive is applied (by guns travelling along a predetermined path to coat each opening device with adhesive, or by simply sliding the opening devices over coating rollers) and/or switching from screw-type to hinged opening devices, normally involves restructuring the entire unit.
Another important factor limiting the versatility of known units is the opening device feed rate to the units necessarily having to match the package feed rate. Which means the speed of the application units is dictated by the longest operation performed on both the opening devices and the packages.
Moreover, both known types of unit are extremely bulky, and have several parts that are accessible only with difficulty by the operator.